Add fast path to _filter_events_for_server
Add fast path to _filter_events_for_server

Most rooms have a trivial history visibility like "shared" or
"world_readable", especially large rooms, so lets not bother getting the
full membership of those rooms in that case.

matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse